#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <set>
#include <stack>
#include <vector>
#include <queue>
#include <map>
#include <cstring>
#include <array>
#include <bitset>
#include <cassert>
using namespace std;
const int maxn=2505;
bitset < maxn > a[maxn];
bitset < maxn > bio[maxn];
int dist1[maxn][maxn];
int dist2[maxn][maxn];
int pref[maxn][maxn];
int uk;
int n, m;
bool provjeri(int x, int y){
for(int i=0; i<n; i++){
bio[i].reset();
}
int val;
queue < pair < int, int > > q;
int br=0;
for(int i=0; i<=n-x; i++){
for(int j=0; j<=m-y; j++){
val=pref[i+x][j+y]-pref[i][j+y]-pref[i+x][j]+pref[i][j];
if(val==x*y){
br++;
q.push({i, j});
dist1[i][j]=0;
dist2[i][j]=0;
bio[i][j]=1;
}
}
}
pair < int, int > p;
int xs, ys;
// cout << "pocetak " << x << ' ' << y << endl;
while(!q.empty()){
p=q.front();
q.pop();
xs=p.first+1;
ys=p.second;
if(!bio[xs][ys] && dist1[p.first][p.second]+1<x){
br++;
bio[xs][ys]=1;
dist1[xs][ys]=dist1[p.first][p.second]+1;
dist2[xs][ys]=dist2[p.first][p.second];
q.push({xs, ys});
}
xs=p.first;
ys=p.second+1;
if(!bio[xs][ys] && dist2[p.first][p.second]+1<y){
br++;
bio[xs][ys]=1;
dist1[xs][ys]=dist1[p.first][p.second];
dist2[xs][ys]=dist2[p.first][p.second]+1;
q.push({xs, ys});
}
}
// cout << br << endl;
return br==uk;
}
vector < array < int, 3 > > svi;
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
cin >> n >> m;
string s;
for(int i=0; i<n; i++){
cin >> s;
for(int j=0; j<m; j++){
pref[i+1][j+1]=pref[i][j+1]+pref[i+1][j]-pref[i][j];
if(s[j]=='1'){
pref[i+1][j+1]++;
uk++;
a[i][j]=1;
}
}
}
int br=0;
int mr=1e9, mc=1e9;
for(int i=0; i<n; i++){
for(int j=0; j<m; j++){
if(a[i][j]){
br++;
}
else if(br){
mr=min(mr, br);
br=0;
}
}
if(br){
mr=min(mr, br);
br=0;
}
}
for(int j=0; j<m; j++){
for(int i=0; i<n; i++){
if(a[i][j]){
br++;
}
else if(br){
mc=min(mc, br);
br=0;
}
}
if(br){
mc=min(mc, br);
br=0;
}
}
assert(mr!=1e9);
for(int i=mc; i>0; i--){
for(int j=mr; j>0; j--){
svi.push_back({i*j, i, j});
}
}
sort(svi.begin(), svi.end());
for(int i=svi.size()-1; i>-1; i--){
if(provjeri(svi[i][1], svi[i][2])){
cout << svi[i][0] << '\n';
return 0;
}
}
return 0;
}
